The most frequently cited conceptual definition of adherence is “the extent to which a person’s behaviour
– taking medication, following a diet, executing lifestyle changes – follows medical advice” (26).
Adherence has also been defined as “the extent to which patient behaviour corresponds with recommendations
from a health care provider” (27,28). It has also been suggested that a more practical
approach is to define adherence as “following treatment at a level above which treatment goals are
likely to be met”. However, these broad definitions belie the complexity of the issue.